The invention relates to a tactile pressure sensor including a body with axially extending bores whose diameters depend on the axial pressure to which the body is subjected so that the axial pressure can be determined by the intensity level of light passing through the bores.
Such a sensor includes a body having opposite end faces and being provided with axial bores through which light is directed from one of the end faces and the light intensity passing through the various bores is recorded and/or passed on at the opposite side. By an axial pressure on the body including the bores, or on the opposite body end faces, the open cross-section of the bores is narrowed so that the light intensity recorded at the exit end of the bores depends on the pressure to which the structure surrounding the bore is subjected. The light intensity measured at the bore exit therefore indicates the pressure load on the body.
DE 195 27 957 discloses a tactile opto-electronic pressure sensor. The tactile part of the sensor consists of an opaque rubber-like body provided with axial collimator bores through which light is directed by an electro-luminescent foil disposed at one end face of the rubber-like body. Under axial pressure load, the width of the axial bores changes. The light passing through the various bores is conducted from the exit end of the bores or its intensity is directly measured by opto-electronic means so that the pressure on the body can be represented topographically by a dot raster.
The disadvantage of such a tactile sensor structure is that the open width of the bores is not only affected by the pressure, but that there are also transverse deformations of the bores caused by the axial pressure: From the location of the maximum axial surface pressure, the rubber-like material is pressed radially outwardly so that the surrounding bores are being curved outwardly from the area where the highest pressure is effective. The curvature of these bores reduces straight light transmission through the bores so that the force results obtained from measuring the light passing through those curved bores are falsified.
The determination of matrix-like arranged light conductors eliminates such transverse force influences. EP 0 328 703 A1 discloses such an arrangement wherein local pressures can be determined with an accuracy depending on the rastor resolution. In a matrix including a plurality of light conductors, the cross-section of the light conductors changes with radial pressure application so that the light transmission through the light conductors in the matrix changes with the radial pressures to which the light conductors are subjected, as it occurs in the fiber optic sensor according to DE 32 36 435 C2. The principle is based on the reduction of light transmission in a light transmitting passage by constriction under the influence of the pressure forces.
Such an arrangement however has the disadvantage that the elements of the matrix can be read only successively by addressing the various matrix elements (light conductor intersections).
It is the object of the present invention to provide an opto-electronic sensor or rather a tactile part for such a sensor with an unambiguous correlation between the axial pressure effect on the light input side of a body including light passages and the light intensity at the light exit side of the body and with which the pressure effective on the light input side can be simultaneously determined by measuring the light transmission intensities at the outlet side of the body.